After greedily watching the best part of Firefly in a weekend, I became slightly obsessed and got increasingly frustrated that, having missed the run of Serenity in UK, it was later than advertised in Florence, ran only for a week I had to return to Liverpool on a Thursday. (And it was just that bit out of town that I didn't manage to get to it.)
Now though I did finally see it, and was slightly disappointed. I understand recapping the Tams/crew tensions that were resolved in the Objects in space for the benefit of first-timers. I also get that myth-rewriting can justify airbrushing out the men with hands of blue (too sillysinister and powerful?), but I was irked that Simon here knows more about River's situation right at the beginning than he discovered only in Ariel and later in the series.
But that's nit-picking, just like my "oh, look, Mal is now inexplicably able to defeat the far superior bad guy in hand to hand combat, yawn" concern: more importantly, the grand secret at the heart of it was unconvincing, especially the reactions (personal and political) to it. And a general point that there could be many more secrets was glossed over.
Hrmpf, I guess that's also nitpicking, I guess I just didn't get the same sense of fun, adventure from this as from the series.
You should probably read the three-issue comic book series, one of your gripes gets resolved there (and I won't spoil it for you by telling you which one
You're right, the film had some major plotholes and most of the TV episodes are better (plot-wise). But I think that's because of the high standard the series set. Serenity is still one of the best SciFi movies to come out in the last decade IMO and among the top-ten space-operas of all time.